This application relates to the control of a refrigerant system, and in particular, to the control of indoor fan operation to prevent moisture being re-evaporated from evaporator external surfaces and then being delivered by indoor airflow into a conditioned environment, when a refrigerant compressor is shut down or during system startup.
Refrigerant systems are utilized to condition the air being delivered into an indoor environment. As an example, an air conditioning system or a heat pump is utilized to cool and dehumidify or heat air being delivered into the environment to be conditioned.
In recent years, significant attention has been paid to indoor air quality issues. In particular, precise control of the indoor relative humidity within the comfort zone has been the subject of an increased scrutiny. In part, this desired humidity control is attributed to prevention of mold, bacteria and fungus formation and growth.
As known, refrigerant systems operate at part-load conditions for most of their design life. Thus, the system operates in a start-stop mode quite frequently to satisfy the demanded sensible and latent capacity requirements, when all other means of system unloading are already exhausted. When the system is operating in a cooling mode, an evaporator that cools and dehumidifies the air being delivered into the indoor environment has cold external surfaces. Moisture forms on the cold external surfaces of the evaporator heat exchanger, while the cooled and dehumidified air flows through the heat exchanger and into the conditioned space. This moisture is removed from the air stream and continuously drained into a drain pan. When the system is shut down, there is often a significant amount of moisture accumulated on the evaporator external surfaces. As the evaporator is gradually warming up, this moisture re-evaporates and is re-introduced into the indoor airstream and consequently into the conditioned environment, since in many application cases, the indoor fan has to operate continuously to comply with legislation and regulation requirements.
Even with the indoor fan shut down simultaneously with other system components, such as a compressor, at system startup, a burst of moist air will often be supplied to the indoor environment causing undesired high humidity fluctuations and consequent occupant discomfort. Additionally, this moisture accumulated on the evaporator external surfaces will promote mold, bacteria and fungus formation and growth. It has become an industry practice to treat external evaporator surfaces with anti-microbial compounds, or employ UV lights to prevent growth of microorganisms. These measures are associated with design complexities and additional costs.
Thus, it would be desirable to provide a solution to the problems mentioned above that does not have the drawbacks of the prior art.